/*
 * Copyright (C) 2006 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.util.concurrent;

import static com.google.common.base.Preconditions.checkState;
import static com.google.common.collect.Lists.newArrayListWithCapacity;
import static java.util.Collections.unmodifiableList;

import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Optional;
import com.google.common.collect.ImmutableCollection;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import java.util.List;
import javax.annotation.Nullable;

/**
 * Aggregate future that collects (stores) results of each future.
 */
@GwtCompatible(emulated = true)
abstract class CollectionFuture<V, C> extends AggregateFuture<V, C> {

    abstract class CollectionFutureRunningState extends RunningState {
        private List<Optional<V>> values;

        CollectionFutureRunningState(ImmutableCollection<? extends ListenableFuture<? extends V>> futures,
                boolean allMustSucceed) {
            super(futures, allMustSucceed, true);

            this.values = futures.isEmpty() ? ImmutableList.<Optional<V>>of()
                    : Lists.<Optional<V>>newArrayListWithCapacity(futures.size());

            // Populate the results list with null initially.
            for (int i = 0; i < futures.size(); ++i) {
                values.add(null);
            }
        }

        @Override
        final void collectOneValue(boolean allMustSucceed, int index, @Nullable V returnValue) {
            List<Optional<V>> localValues = values;

            if (localValues != null) {
                localValues.set(index, Optional.fromNullable(returnValue));
            } else {
                // Some other future failed or has been cancelled, causing this one to also be
                // cancelled or
                // have an exception set. This should only happen if allMustSucceed is true or if
                // the output
                // itself has been cancelled.
                checkState(allMustSucceed || isCancelled(), "Future was done before all dependencies completed");
            }
        }

        @Override
        final void handleAllCompleted() {
            List<Optional<V>> localValues = values;
            if (localValues != null) {
                set(combine(localValues));
            } else {
                checkState(isDone());
            }
        }

        @Override
        void releaseResourcesAfterFailure() {
            super.releaseResourcesAfterFailure();
            this.values = null;
        }

        abstract C combine(List<Optional<V>> values);
    }

    /** Used for {@link Futures#allAsList} and {@link Futures#successfulAsList}. */
    static final class ListFuture<V> extends CollectionFuture<V, List<V>> {
        ListFuture(ImmutableCollection<? extends ListenableFuture<? extends V>> futures, boolean allMustSucceed) {
            init(new ListFutureRunningState(futures, allMustSucceed));
        }

        private final class ListFutureRunningState extends CollectionFutureRunningState {
            ListFutureRunningState(ImmutableCollection<? extends ListenableFuture<? extends V>> futures,
                    boolean allMustSucceed) {
                super(futures, allMustSucceed);
            }

            @Override
            public List<V> combine(List<Optional<V>> values) {
                List<V> result = newArrayListWithCapacity(values.size());
                for (Optional<V> element : values) {
                    result.add(element != null ? element.orNull() : null);
                }
                return unmodifiableList(result);
            }
        }
    }
}
